The invention relates a new family of non-ionic surfactants and, more specifically, to alkyl cyclohexanol alkoxylates and a method for making same.
Non-ionic surface active agents and their preparation are generally known in the art. U.S. Pat. Nos. 2,174,761; 2,674,619; and 2,677,700 teach non-ionic surfactant compositions prepared by the addition of ethylene oxide and propylene oxide to a reactive hydrogen compound. It is known in the art to make non-ionic surfactants from numerous starting hydrophobes, such as alkylated phenols, fatty alcohols, fatty acids, etc. This family of surfactants has numerous end uses, such as foam control agents, wetting agents, scouring agents for cleaning formulations, emulsifiers, de-emulsifiers, dispersants, synthetic lubricants, and any application where surfactantcy, lubricity, and foam control are important. Ethoxylated nonylphenol, in particular the nine to twelve mole ethoxylate, has achieved a dominant position in the worldwide surfactant market as the non-ionic surfactant of choice because of its excellent surfactant properties, low odor, ease of use due to lower pour points and lower chill points, and low costs compared to other non-ionic surfactants.
In the recent years, alkylphenol alkoxylates, such as ethoxylated nonylphenol, have been criticized for having poor biodegradability, high aquatic toxicity of the byproducts of the biodegradation of the phenol portion, and there is an increasing concern that these chemicals act as endocrine disrupters. Some studies have shown there to be links between alkylphenols and declining sperm count in human males and there is evidence that alkylphenols may harmfully disrupt the activity of human estrogen and androgen receptors.
Concern over the environmental and health impact of alkoxylated alkylphenols has led to governmental restriction on the use of these surfactants in Europe, as well as voluntary industrial restrictions in the United States. Many industries have attempted to replace these preferred alkoxylated alkylphenol surfactants with alkoxylated linear and branched alkyl primary and secondary alcohols, but have encountered problems with odor, performance, formulating, and increased costs. The odor and some of the performance difficulties of the alkoxylated alkyl alcohols are related to the residual free alcohol, which is the portion of the reactant alcohol that does not react with alkylene oxide during the alkoxylation step.
The presence of the unreacted free alcohol is due to the reaction kinetics of alkoxylating an alcohol under a base catalysis in which a nucleophilic attack by RO.sup.- occurs at a ring carbon atom of the alkylene oxide. For example, the product distribution of ethoxylating under basic conditions is determined by the relative rates of two steps and the relative acidities of the alcohol and its ethylene oxide adducts. ##STR1## This relative acidity becomes important in determining the equilibrium constant for the proton exchange reaction between the starting alcohol and its ethylene oxide adducts. EQU ROH+[RO--CH.sub.2 --CH.sub.2 --O].sup.- .revreaction.[RO].sup.- +RO--CH.sub.2 --CH.sub.2 --OH
When the acidity of ROH is slightly less than that of its corresponding oxide adduct, such as with a linear or branched alkyl alcohol, the equilibrium constant for the proton exchange reaction will be less than or equal to 1. Because formation of any specific anion is not strongly favored, the chain extension of the alcohol oxide adduct will occur well before the original ROH undergoes reaction.
When the acidity of ROH is greater than that of its corresponding oxide adduct, such as with a phenol, the equilibrium constant for the proton exchange reaction will be much larger than 1. Even when there is an excess of ethylene oxide, chain extension does not occur until substantially all of the ROH has reacted to form the monoadduct. Aqueous acid ionization constants for various alcohols and their adducts are approximately 10.sup.-9 for phenol, 10.sup.-15 for phenol ethylene oxide adducts, 10.sup.-16 for alkyl alcohols and 10.sup.-15 for alkyl alcohol ethylene oxide adducts.
The impact of the equilibrium constant for the proton exchange reaction could result in 15% to 40% unreacted alcohol in a linear primary or secondary alcohol system even after four moles of ethylene oxide (EO) have been reacted. This residual "free alcohol" not only negatively impacts the surfactant and formulating properties of an alkoxylated alkyl alcohol but increases irritation of eyes and skin associated therewith and gives the alkoxylated alkyl alcohol the strong offensive odor of the starting alcohol. Efforts to resolve these problems are taught in U.S. Pat. No. 4,210,764, in which BaO and cresylic acid are used as the catalyst system; U.S. Pat. No. 4,223,164, in which basic compounds of strontium in the presence of phenol are used as the catalyst; U.S. Pat. No. 4,453,022, in which Ca(OEt).sub.2 is the catalyst; and U.S. Pat. No. 4,754,075, in which CaO and an activator, such as a glycol, is the catalyst system in which the ethoxylation of alkyl alcohols results in narrow range or peaked ethoxylates. These peaked or narrow range ethoxylated alcohols, with lower levels of free alcohol, show some improvement in overall surfactant properties, but problems of odor, high cost, and ease of formulating still remain a problem.
Typical capillary GC results to determine the percentage of free alcohol on a one, four, and six mole ethoxylate of a nonylphenol using a basic catalyst, of a lauryl alcohol using a basic catalyst, and of a lauryl alcohol using a "peaking" catalyst are as follows:
TABLE 1 ______________________________________ % FREE ALCOHOL Hydrophobe/ One mole Four mole Six mole Catalyst Ethylene Oxide Ethylene Oxide Ethylene Oxide ______________________________________ Nonylphenol/ 0.05 0.01 &lt;0.01 NaOH Lauryl Alcohol/ 64.5 23.2 13.8 NaOH Lauryl Alcohol/ 21.5 8.1 5.2 CaO (peaking) ______________________________________
Other approaches to produce environmentally friendly, low odor, non-endocrine disrupting surfactants include use of alkyl polyglycosides, glucoamine, carboxylated nonionics, ethoxylated amines, amphoterics, and N-methyl glucosamide. Although these approaches have achieved improved ecological, non-endocrine disrupting properties, the overall surfactant properties are generally poor, formulating is difficult, and costs are anywhere from 20% to 150% higher than costs associated with using alkylphenol alkoxylates.
Other methods to produce environmentally friendly surfactants are discussed in U.S. Pat. Nos. 3,859,324, 3,953,522, and 3,953,523, in which methods are shown to produce n-alkyl substituted hydroxypolyalkoxymethylcyclohexenes and n-alkyl substituted hydroxypolyalkoxymethylcyclohexanes. These methods involve a Diels-Alder condensation of butadiene with allyl alcohol. The resulting hydroxymethylcyclohexene is then placed in the presence of a free radical generating compound alkylated with an alpha olefin to form an alkyl substituted hydroxymethylcyclohexene, which is then hydrogenated and alkoxylated to form a nonionic surfactant. However, the performance of the resulting nonionic product not only suffers from problems associated with a large percentage of unalkoxylated n-alkyl substituted hydroxymethylcyclohexane, but the process of alkylation will also yield a large percentage of polyalphaolefins, which are highly branched hydrocarbons, that negatively impact surfactant properties.